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AASHTO Stantard Specification LFD Live Load Impact for Truss Member

AASHTO Stantard Specification LFD Live Load Impact for Truss Member

AASHTO Stantard Specification LFD Live Load Impact for Truss Member

(OP)
I am doing Load Factor Rating for Truss Bridge. The section 3.8.2.1 of AASHTO Standard specification defines Live Load Impact as 50/(L+125), where L is the length in feet of the portion of the span that is loaded to produce the maximum stress in the member. For a truss member (compression or tension) how can L be calculated? In my understanding as an example For HS-20 Truck, the length of the truck 14'+14'= 28ft(using the minimum length from 14ft to 30ft ) is portion of span that is loaded to produce maximum load on truss member.Am I correct or is there any other way of determining 'L'?

Thank you for your help.

RE: AASHTO Stantard Specification LFD Live Load Impact for Truss Member

L for the impact factor is the length of the truss, not the lengths of individual members.

RE: AASHTO Stantard Specification LFD Live Load Impact for Truss Member

You may need to construct influence line to find L (length of positive or negative area).

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